Ball seat system

ABSTRACT

The system and method for hydraulic fracturing includes a downhole tool with a sub, a sleeve, a ball seat support, and a ball seat holder. A ball dropped through the wellbore sits on the ball interface of the ball seat holder. Fluid flowing through the system pushes the ball against the ball interface, causing the ball seat holder to slide through the ball seat support and the ball interface to clamp the ball. A ball matches only a particular ball interface. Additional pressure forms a seal of the ball, the ball seat holder, and the ball seat support and moves the sleeve to slide through the sub and expose the throughbore to the annulus for the fracturing. Contact distributed between the ball, ball interface of the ball seat holder, and ball seat support withstands the temperature and pressure of the fracturing without deformation or failure of the ball.

RELATED U.S. APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO MICROFICHE APPENDIX

Not applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a system for multi-stage fracturing with a multiple downhole tools within a wellbore. More particularly, the present invention relates to downhole tools with a ball seat system to withstand temperatures and pressures of hydraulic fracturing. Even more particularly, the present invention relates to a ball interface between the ball and ball seat support of a downhole tool.

2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98

The process of fracking, also known as induced hydraulic fracturing, involves mixing sand and chemicals in water to form a frac fluid and injecting the frac fluid at a high pressure into a wellbore. Small fractures are formed, allowing fluids, such as gas, petroleum, and brine water, to migrate into the wellbore for harvesting. Once the pressure is removed to equilibrium, the sand or other particle holds the fractures open. Fracking is a type of well stimulation, whereby the fluid removal is enhanced, and well productivity is increased.

Multi-stage hydraulic fracturing is an advancement to harvest fluids along a single wellbore or fracturing string. The fracturing string, vertical or horizontal, passes through different geological zones. Some zones do not require harvesting because the natural resources are not located in those zones. These zones can be isolated so that there is no fracking action in these empty zones. Other zones have the natural resources, and the portions of the fracturing string in these zones are used to harvest from these productive zones.

In a multi-stage fracking process, instead of alternating between drilling deeper and fracking, a system of ball-drop frac sleeves and packers are installed within a wellbore to form the fracturing string. The sleeves and packers are positioned within zones of the wellbore. Fracking can be performed in stages by selectively activating sleeves and packers, isolating particular zones. Each target zone can be fracked stage by stage without the interruption of drilling more between stages.

Frac balls are the known prior art in a multi-stage fracking process. FIG. 1 is a schematic view of a prior art ball-activated sleeve system 100. There are ball seats 112, 114 and 116 with corresponding sleeves 118, 120 and 122. The smallest frac ball 130 is dropped through ball seat 116, then ball seat 114, and rests in ball seat 112. Frac fluid through frac ports 136 builds pressure as the frac ball 130 plugs ball seat 112. The pressure moves the sleeve 118 to expose the open hole 124 to the frac fluid for fracturing the wellbore at the depth of open hole 124. Next, the next sized frac ball 132 is dropped through ball seat 116 and rests in ball seat 114. Frac fluid through frac ports 138 builds pressure as the frac ball 132 plugs ball seat 114. The pressure moves the sleeve 120 to expose the open hole 126 to the frac fluid for fracturing the wellbore at the depth of open hole 126. Then, the next largest sized frac ball 134 is dropped through ball seat 116 and rests in ball seat 116. Frac fluid through frac ports 140 builds pressure as the frac ball 134 plugs ball seat 116. The pressure moves the sleeve 122 to expose the open hole 128 to the frac fluid for fracturing the wellbore at the depth of open hole 128. The fracturing string harvests fluids stage by stage, with each stage requiring a different, slightly larger sized frac ball and corresponding ball seat. Setting the order of stages is very important, so the balls and ball seat must be carefully maintained in sequential order and sequential sizes.

There are problems with the prior art multi-stage system and method. To increase the number of stages, the number of sets of ball and ball seat must also increase. However, the diameter of the ball cannot continue to increase in order to add another stage. Instead, the incremental increase between balls must be reduced further and further. Fine differences in diameter of the ball, as little as 1/16 inch, can separate successive balls in the multi-stage system. With the narrow tolerances for the size of frac balls, excessive pressure can cause slight deformations with significant consequences. Even slight deformations may cause one ball to be confused for another size ball. In multi-stage fracturing, the ball seat system is exposed to high pressures for longer periods of time. The risk of deformation due to excessive pressure is a problem of maintaining the ball to ball seat seal.

In the past, various multi-stage sleeve systems have been developed to change the ball to ball seat seal. United States Patent Publication No. 20120061103, published for Hurtado et al. on Mar. 15, 2012 teaches a ball seat system for multiple frac balls. The ball seat system has two ball seats for two same size frac balls. The dual ball system triggers the sleeve. United States Patent Publication No. 20130220603, published for Robison et al. on Aug. 29, 2013, describes a system with a flow sensor to detect a number of balls or darts passing through the tool. Once a set number of balls have passed the sensor, the sleeve triggers. The number of balls determines the triggering, not the size or sequence of balls. United States Patent Publication No. 20110240311, also published for Robison et al. on Oct. 6, 2011, is a variation with an insert hydraulically activated when the set number of balls is detected by the sensor. The insert triggers the sleeve.

Other variations on the multi-stage systems include United States Patent Publication No. 20120312557, published to King on Dec. 13, 2012, disclosing a sleeved ball seat. The sleeved ball seat system is ball and a ball seat, wherein the ball blocks fluid flow as a flow restrictor. The flow continues and gradually closes the sleeve ports. The ball to ball seat seal is no longer relevant to the trigger of the sleeve. United States Patent Publication No. 20130161017, also published for King on Jun. 27, 2013, has a sleeved ball seat system with the ball triggering the ball seat to shift. The shift opens the sleeve and allows the ball to pass to the next tool. Again, the ball and ball seat seal is no longer relevant to the trigger and fluid pressure. The shift now maintains the seal and pressure.

FIG. 2 shows a prior art system for hydraulic fracturing. There is the system 150 with a downhole tool 152, such as a frac sleeve. There is a top sub 154 and a bottom sub 156 in a wellbore with an opening 168 for access to the formation. A ball seat 158 sits in a sliding sleeve 164 at the end of the top sub 154. The sliding sleeve 164 covers the opening 168 in the first position so that the access to the formation is covered. A ball 160 is dropped through the wellbore to sit in the ball seat 158, forming a seal 162 against the surface of the ball 160 and an edge of the ball seat 158. Once seating, frac fluid from the top pushes against the ball 160 and ball seat 158 to move the sliding sleeve 164 toward the bottom sub 156. As the sliding sleeve 164 moves, the opening 168 is exposed to the frac fluid. The frac fluid can be dispensed at high temperature to the formation through the opening 168. The seal between the ball 160 and ball seat 162 maintains the pressure for fracturing the formation. The seal 162 is subject to wear, especially at high temperatures and pressures of the frac fluid and especially for longer periods of exposure to the high temperatures and pressures (greater than 300 degrees F. and 10,000 psi.

The ball 160 can fail and break. At the edge of the seal 162, there can be deformation, affecting the size of the ball 160 and breaking the seal 162. Also, the broken seal reduces the amount of pressure that can be maintained for the fracturing. Breaking and leaking are problems of the prior art systems.

It is an object of the present invention to provide a ball seat system for a multi-stage hydraulic fracturing system.

It is another object of the present invention to provide a ball seat system with a ball seat holder.

It is another object of the present invention to provide a ball seat system with an improved seal between the ball and the ball seat.

It is still another object of the present invention to provide a ball seat system with a seal between the ball and ball seat to withstand greater fracturing pressures.

It is still another object of the present invention to provide a ball seat system with a ball seat holder to hold more pressure than the ball and ball seat.

It is yet another object of the present invention to provide a ball seat system with an improved seal without affecting the size and sequence of frac balls in a multi-stage fracturing.

These and other objectives and advantages of the present invention will become apparent from a reading of the attached specifications and appended claims.

SUMMARY OF THE INVENTION

Embodiments of the system and method for hydraulic fracturing of the present invention include a downhole tool with a sub, a sleeve, a ball seat support, and a ball seat holder. A ball is dropped through the wellbore to sit on the ball seat holder, triggering the activity of the system. The sub has an upper portion and lower portion, and the sleeve slides between the two portions. A throughbore extends longitudinally through the sub and sleeve for fluid flow. The ball seat support has an anchoring surface fixedly engaged to the sleeve so that the ball seat support can actuate movement of the sleeve. The opposite side of the ball seat support is a seating surface. Fluid flows through the ball seat support through the support throughbore and through the seat support opening at the end of the seating surface. The ball seat holder is housed in the ball seat support with the ball seat holder engaging the seating surface. Fluid can also flow through the ball seat holder through the holder throughbore and through the holder opening at the end of the ball seat holder.

The ball seat holder can be comprised of a mounting member and a ball interface. The ball interface contacts the ball dropped into the wellbore. The ball has a size corresponding to the ball interface, such that each ball matches a particular ball interface of a particular ball seat holder. The ball triggers the formation of a seal with the ball, ball seat holder, and the ball seat support. The seal of the embodiments of the present invention are stronger and more durable and more versatile than the seals formed in the prior art.

Embodiments of the ball seat support of the present invention include the seating surface being comprised of a cylindrical portion and a tapered portion. The ball and the ball seat holder fit through the cylindrical portion. The tapered portion decreases in diameter from the cylindrical portion to the seat support opening, such that the seat support opening is at the end of the tapered portion. The tapered portion can be conical, arcuate, curved or other shape with a decreasing diameter from the cylindrical portion to the seat support opening. There is a defined boundary between the cylindrical portion and the tapered portion. The ball seat holder slides through the cylindrical portion and abuts against this boundary, which holds the ball seat holder against the tapered portion.

There are also embodiments of the ball seat holder disclosed. The mounting member is generally cylindrical for being disposed within the ball seat support, in particular a cylindrical portion of the ball seat support. In some embodiments, there is a seat shearing means removably attached to the seating surface of the ball seat support. A shearing means, such as a shear pin or spring, extends between an exterior of the mounting member and the cylindrical portion of the seating surface. The shearing means ruptures to release movement of the ball seat holder towards the seat support opening. Fluid pressure against the ball seat holder causes the shearing action.

Another aspect of the ball seat holder is the ball interface. In some embodiments, the ball interface is comprised of a collet collar. The collet collar has a clamping or collapsing action as pressure is exerted on the ball by fluid flow. In the collet collar embodiment, the mounting member is a sleeve portion, the ball interface is a clamp portion, and the holder opening is a collet opening at an end of the collet collar. The collet opening has a size corresponding to the size of the ball to be received with the ball seat holder. The action of the collet collar begins in an extended position for receiving the ball with the sleeved portion in a front end of a cylindrical portion of the seating surface of the ball seat support. Once the ball is seated on the collet collar, the ball exerts pressure on the collet collar by fluid flow against the ball. At sufficient pressure, the sleeved portion shears from the cylindrical portion, and the collet collar moves through the ball seat support along the seating surface toward the seat support opening. Movement of the sleeved portion stops at the boundary between the cylindrical portion and the tapered portion of the seating surface. The sleeved portion is cylindrical and cannot pass through the decreasing diameter of the tapered portion. The fluid flow and pressure continues, exerting more pressure on the ball against the clamp portion, which collapses solid to the collet opening, stopping fluid flow through the collet collar with the ball. The holder throughbore is sealed from fluid flow, and the support throughbore is sealed from fluid flow. The seat support opening is filled with the ball and the clamp portion of the collet collar. As pressure builds, the ball seat support begins to move the sleeve, opening the throughbore to the annulus. Additional fluid flow presses the seal solid, and the fluid flow can increase in temperature and pressure to effect the fracturing activity.

In still another embodiment, the ball interface is comprised of tapering collet petals, each petal being separated by slits. The reduction and elimination is the narrowing and closing of the slits between the petals. The slits are between the petals laterally, or they may overlap petals for slits between and over adjacent petals.

For a multi-stage process, the system includes a second downhole tool with a second ball seat support and a second ball holder. The second ball interface on the second ball holder corresponds to a second ball. The second ball size matches the second ball interface, which is different from the first ball interface. The first and second ball sizes are not the same. Different size balls trigger different tools, so that the multi-stage process is possible to trigger in a controlled order.

Embodiments of the present invention include the method for multi-stage hydraulic fracturing. The system is used to perform the fracturing. The steps include installing a downhole tool with the system of the present invention and flowing fluid through the throughbore, support throughbore, and the holder throughbore. Then, a ball of a set size is dropped through the wellbore. The ball is seated on the ball interface of the ball seat holder with the matching size. Additional fluid flow exerts pressure on the ball against the ball seat holder, moving the ball seat holder through the ball seat support. Next, the ball is sealed to the ball interface, and the ball seat holder is sealed to the ball seat support so as to stop fluid flow through the holder opening, the ball interface, and the seat support opening. More fluid flow exerts pressure on the ball seat support to slide the sleeve toward the lower portion of the sub. The frac ports are now open for performing the fracturing activity. The improved seal withstands the temperature and pressure of the fracturing.

After completing a fracturing at one location, embodiments of the method further include dropping another ball of another set size through the wellbore. The set size of another ball is different from the set size of the original ball, so a different downhole tool is activated. The other ball engages another ball interface to trigger another opening of frac ports in a second location. There can be fracturing at another frac port at a pressure maintained by sealing the other ball to the other ball interface and the other ball seat holder to the other ball seat support of the other downhole tool.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a prior art multi-stage hydraulic fracturing system, being placed in a wellbore.

FIG. 2 is another schematic view of a downhole tool in the wellbore with the prior art ball seat and sliding sleeve.

FIG. 3 is another schematic view of a downhole tool in the wellbore with the embodiments of the present invention for the ball seat system.

FIG. 4 is a cross-sectional view of an embodiment of the system for hydraulic fracturing, showing the ball seat holder in an initial extended position.

FIG. 5 is a cross-sectional view of an embodiment of the system for hydraulic fracturing, showing the ball seat holder in a sealed retracted position.

FIG. 6 is an exploded perspective view of another embodiment of the ball seat holder of the present system.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to FIGS. 3-5, the system 10 for hydraulic fracturing, comprises a sub 12, a sleeve 14, a ball seat support 16, and a ball seat holder 18. The sub 12 is any part of a downhole tool, such as a packer, plug, or frac sleeve. The sub 12 includes any downhole tool that has used a ball-to-ball seat connection as a trigger. The system 10 is placed by a drill string, production string, coiled tubing or other means, within a wellbore 22. Multiple systems 10 can be placed down the wellbore 22 as well. The multiple systems 10 provide for multi-stage hydraulic fracturing because each system 10 can be triggered separately in a controlled manner. For example, more than one zone of the formation can be fracked in the wellbore 22 without additional drilling between fracking operations. The systems 10 can be placed at particular depths and in particular zones. Any downhole tool with a ball to ball seat interaction can be compatible with the system 10 of the present invention. A ball 20 is dropped through the wellbore 22 to sit on the ball seat holder 18, triggering activity of the system 10.

The sub 12 can be incorporated into any downhole tool and has an upper portion 24 and lower portion 26. A throughbore 28 extends longitudinally through the sub 12 from the upper portion 24 to the lower portion 26, and fluid flows through the system 10 through this throughbore 28. The upper portion 24 and the lower portion 26 can be connected by any known mechanical means, such as screw threads, welding or composite construction. The sub 12 can have port openings 30 in FIG. 3. The port openings 30 make a fluid connection between the annulus and formation 32 and the throughbore 28.

The sleeve 14 slides between the upper portion 24 and lower portion 26. The throughbore 28 also extends longitudinally through the sleeve 14 for fluid flow, as shown in FIG. 3. The sleeve 14 has a first position, covering the port openings 30 to seal the annulus from the throughbore 28. There is a sealed barrier formed by the body of the sleeve 14 across the port opening 30. The sleeve 14 has a second position, exposing the port openings 30 to make a fluid connection between the annulus and the throughbore 28. The sealed barrier is removed in this second position. This fluid connection allows the hydraulic fracturing to happen. The frac fluid pumped through the throughbore 28 enters the annulus and formation 32 at a high temperature and high pressure to accomplish the fracturing of the relevant zone within the earth.

In some embodiments, the sleeve 14 can have a sleeve shearing means 34, as shown in FIG. 3. In the first position, the sleeve 14 is aligned with upper portion 24, locked by sleeve shearing means 34 relative to the sub 12. Sleeve shearing means 34 can be comprised of shear pins, springs, or other mechanical elements for removably holding the sleeve 14 in place relative to the sub 12. The shearing means 34 removably attached to the upper portion 24 of the sub 12 and an exterior of the sleeve 14. Fluid pressure exerted on the sleeve 14 directly or other elements connected to the sleeve 14, pushes the sleeve 14 toward the lower portion 26. As the sleeve 14 moves, the sleeve shearing means 34 releases or ruptures as the sleeve 14 moves from the first position to a second position. The resistance of the sleeve shearing means 34 can be overcome by pressure exerted on the sleeve 14. As the sleeve 14 moves, the port openings 30 are opened to make a fluid connection between the annulus and formation 32 and the throughbore 28, through the port openings 30 of the sub and throughbore 28. The port openings 32 are exposed for the introduction of frac fluid in the fracturing operation.

In still another embodiment of the system 10, the sleeve 14 can have sleeve ports, which are holes in the sleeve 14. The first position of the sleeve 14 with sleeve ports corresponds to misalignment of the sleeve ports with the port openings 30. The second position of the sleeve 14 with sleeve ports corresponds to alignment of the sleeve ports with the port openings 30. Instead of being pushed away from the port openings 30, alternate embodiments include a sleeve 14 with sleeve ports to align and open the fluid connection. Sleeve ports can be an option for longer sleeves. The sealed barrier between the throughbore 28 and the annulus and formation 32 is the misalignment of the port openings 30 with the sleeve ports.

FIGS. 4-5 also show ball seat system embodiments of the ball seat support 16 and the ball seat holder 18. The ball seat support has an anchoring surface 36 fixedly engaged to the sleeve 14 so that the ball seat support 16 can actuate movement of the sleeve 14. The anchoring surface 36 abuts a shoulder of the sleeve 14. Movement of the ball seat support towards the lower portion 26 corresponds to movement of the sleeve 14 toward the lower portion 26. Pressure exerted on the ball seat support 16 can result in movement of the sleeve 14. The opposite side of the ball seat support 16 is a seating surface 38. Fluid flows through the ball seat support 16 through the support throughbore 40 and through the seat support opening 42 at the end of the seating surface 38. The support throughbore 40 is in fluid connection with the throughbore 28. In the prior art, including FIG. 2, direct contact of the ball to the seat support opening triggered the activity of the system. The ball to seat support opening had to withstand all temperatures and pressures at this one contact point. In contrast, embodiments of the seating surface 38 include a cylindrical portion 44 and a tapered portion 46. The tapered portion 46 decreases in diameter from the cylindrical portion 44 to the seat support opening 42. The section of the seating surface 38 in the tapered portion 46 can be conical, arcuate, curved or other tapered formation. FIGS. 4-5 show the tapered portion 46 as generally conical.

FIG. 6 shows a perspective view of the ball seat holder 18 as presented in FIGS. 3-5. The ball seat holder 18 is housed in the ball seat support 16 with the ball seat holder 18 engaging the seating surface 38. At least a portion of the ball seat holder 18 is adjacent the seating surface 38. There is a holder throughbore 48 so that fluid can also flow through the ball seat holder 18 and through the holder opening 50 at the end of the ball seat holder 18. There is fluid connection between the holder throughbore 48, the support throughbore 40, and the throughbore 28. In some embodiments, shown in FIG. 4, there is a seat shearing means 52 for attaching between the seating surface 38 and the exterior of the ball seat holder 18. Similar to the sleeve shearing means 34, the seat shearing means 52 releases and ruptures upon exertion of sufficient pressure. The seat shearing means 34 can be comprised of springs, shear pins, or other known mechanical devices. The ball seat holder 18 is then able to move within the ball seat support 16, along the seating surface 38, and toward the seat support opening 42.

FIGS. 4-6 shown an embodiment of the ball seat holder 18 comprised of a mounting member 54, and a ball interface 56. The holder opening 50 is at an end of the ball interface 56. The ball seat holder 18 is malleable and flexible. The ball interface 56 is deformable at high temperatures and pressures. In embodiments with the seats shearing means 52, the exterior of the mounting member 54 is removably attached to the seating surface 38 of the ball seat support 16. The ball interface 56 has a size corresponding to a size of a ball 20 to be received within the ball seat holder 18. Only a particular size ball fits a particular ball seat holder so that the multi-stage fracturing can be controlled. A known ball seat holder 18 in a particular zone can be targeted so that the ball 20 with the corresponding size is dropped to trigger activity in that zone. In embodiments of the present invention, a seal is formed between the ball 20 and the ball seat holder 18 and the ball seat support 16. The seal is stronger and more reliable than the ball to ball seat seal of the prior art.

Embodiments of the present invention include the ball seat holder 18 as a collet collar 60. As shown in FIG. 6, the mounting member 54 is a sleeve portion 62, and the ball interface 56 is a clamp portion 64. The holder opening 58 remains at the end of the collet collar 60, as a collet opening 66. The size of the collet opening 66 corresponds to the size of the ball 20 to be received with the ball seat holder 18 with the collet collar 60 as the ball interface 56. In an extended position for receiving the ball 20, the sleeve portion 62 is disposed in a front end of a cylindrical portion 44 of the seating surface 38. The ball 20 is not seated yet, and fluid flows through the throughbore 28, support throughbore 40, and holder throughbore 50. In some embodiments, the seat shearing means 52 holds the ball seat support 16 and ball seat holder 18 together.

After the ball 20 is dropped and is seated on the collet collar 60, there is a transitioning position to reduce the fluid flow through the support throughbore 40 and the holder throughbore 50. The ball 20 engages the collet collar 60 at the collet opening, impeding fluid flow. Fluid flow exerts pressure on the ball 20 against the collet collar 60. Pressure builds until the ball seat holder 18 starts moving along the seating surface 38 of the ball seat support 16. In some embodiments, the movement starts when the seat shearing means 52 is ruptured. The ball seat holder 18 moves toward the seat support opening 42 exerting pressure from fluid flow on the collet collar 60. As the ball seat holder 18 moves into the tapered portion 56, the fluid flow through the holder throughbore 50 and the support throughbore 40 diminishes, increase the pressure on the ball 20 as fluid tries to pass through smaller and smaller passageways.

The increased pressure of the ball 20 causes a clamping action of the ball interface 56 or clamp portion 64 of the collet collar 60. The collet collar 60 moves through the ball seat support 16, until the sleeve portion 54 abuts against the seating surface 38, where the cylindrical portion 44 meets a tapered portion 46. As seen in FIGS. 4 and 5, the clamp portion 64 stretches along the tapered portion 46 of the seating surface 38. The boundary of the cylindrical portion 44 and tapered portion 46 anchors the sleeve portion 54 so that the clamp portion 56 can clamp. The contacts against the ball 20 by the clamp portion 64 clamp down on the ball 20. The clamp portion 64 becomes flush against the tapered portion 46 of the seating surface 38. The fluid flow is gradually eliminated as the ball 20 is pressed against the ball interface 56 to seal against the seating surface 38. The ball 20 to ball interface 56 to ball seat support 16 form a seal. The ball 20 engages the collet opening 66, not the seat support opening 42. The additional strength and contact area of the collet opening 66 increases reliability and strength of the seal against fluid flow.

The collet collar 60 reaches a retracted position for sealing the ball 20, ball seat holder 18, and the ball seat support 16, when the clamping portion 64 makes the narrowest collet opening 66. The ball 20 remains seated at the strongest seal at this position. The holder throughbore 50 is sealed from fluid flow, the collet opening 66 is sealed by the ball, and the seat support opening 42 is sealed by the collet collar 60 and the ball 20.

In some embodiments, the ball interface 56 can be comprised of tapering collet petals 68 as shown in FIG. 6. Each petal 68 is separated by slits 70. When this ball interface 56 is a collet collar 60 or comprised of tapering collet petals 68, fluid flows through the slits 70 or other collapsible passageways in a collet collar 60. Reducing the fluid flow is gradual, not abrupt like the prior art. The present invention extends the working life of the ball 20, ball seat holder 18 and ball seat support 16. In the extended position, fluid flows through the slits 70, the holder opening 58, and the seat support opening 42. The transitioning position closes the slits 70 of adjacent collet petals 68 by narrowing and compressing. In the retracted position or fully clamped position, the fluid flow through the slits 70, the holder opening 58, and the seat support opening 42, stops. The seal is formed with the ball 20, the collet petals 68, and the seat support opening 42.

Other embodiments have the tapering collet petals 68 radially overlap. Each slit 70 is positioned between and over adjacent petals 68, such that the clamping action folds petals over each other. The side space between adjacent petals 68 and lateral space between surfaces of adjacent petals 68 are reduced and closed to form the seal. The petals 68 can be radially overlapping, like the blades of a fan. A seal is made strong by reducing space between the petals in more than one dimension.

The seal of the embodiments of the present invention are stronger and more reliable than the ball to ball seat seal of the prior art. There is additional resistance or interference against the high temperature and high pressures required for fracking. The seal of the ball, ball seat holder, and ball seat support withstand more pressure and gradually adjust to high pressures. The sharp contact of the seat support opening to the ball is reduced by including the holder opening to contact the ball and the tapered portion to contact the seat support opening. The resistance and interference of these structures are greater than prior art systems. There is less risk of failure or deformation of the ball. In the prior art, ⅛ inch thick ring of contact between the ball and ball seat was required to withstand fracturing pressures and temperatures. Thus, ball size was restricted to these minimum amounts to effectively fracture. The number of stages in a multi-stage fracturing was limited by this ⅛ inch thick ring. In the present invention, the amount of contact between the ball and the ball seat is less than the prior art. The ball seat holder allows for ball size increments to be smaller, while maintaining the seal of the proper strength against the fracturing pressures and temperatures. More stages can be added for deeper wellbores, and longer strings can have multi-stage capability.

In yet another embodiment, the system for multi-stage hydraulic fracturing includes at least two sets of structures. There is a first sub, first sleeve, first ball seat support, first ball seat holder, and a first ball. There is a second sub, second sleeve, second ball seat support, second ball seat holder, and a second ball. The sets are nearly identical, except that the balls and ball seat holders are different sizes. The first ball is sized for only the first ball seat holder, and the second ball is sized for only the second ball seat holder. The multi-stage system is controlled by selecting a ball of a particular size to be dropped to engage a corresponding ball seat holder. When the tool with the corresponding ball seat holder is known and at a known zone in the wellbore, the system can choose to fracture at that zone. A different size ball corresponds to a different ball seat holder and different tool at a different zone. The different tools can be turned on and off by dropping different balls. In the present invention, the incremental size differences between balls can be reduced. More stages can be added to the system because more balls of different sizes can be used.

The multi-stage system includes sets of ball seat holders with mounting members and ball interfaces with distinct sizes for interacting specifically with correspondingly sized balls. The same throughbore connects the support throughbore and holder throughbores through the drill string or wellbore. Each tool corresponds to port openings to make a fluid connection or end a fluid connection between the throughbore and the annulus or formation. The ball interfaces may also be collet collars or other structures with collapsing to reduce fluid flow.

Embodiments of the method of the present invention involve the structures of the system 10, shown in FIGS. 3-6. The method for multi-stage hydraulic fracturing, comprising the steps of: installing a downhole tool with the system 10, flowing fluid through the wellbore, dropping a ball 20 of a set size through the wellbore, seating the ball 20 on the ball interface 56, flowing more fluid through the wellbore to elevate pressure of the ball 20 on the ball interface 56, moving the ball seat holder 18 through the ball seat support 16 by the fluid pressure on the ball 20, sealing the ball 20, ball seat holder 18 and ball seat support 16 to stop fluid flow through the throughbore, flowing even more fluid through the wellbore to push the ball seat support 16 against the sleeve 14, sliding the sleeve 14 to make a fluid connection between the throughbore 28 and the annulus and/or formation, and fracturing the formation through the fluid connection of the throughbore 28.

Embodiments of the method further include completing a fracturing at the downhole tool, dropping another ball of another set size through the wellbore, seating another ball on another ball interface, and fracturing the formation at another location in the wellbore. The set size of the ball is different from the other ball to find a particular downhole tool in another location. The same seal of the system 10 is formed at the other downhole tool for fracturing hydraulically through another frac port at the new location.

The downhole tool includes the sub 12 with an upper portion 24 and lower portion 26. The sub 12 is the tool body for any downhole tool, such as a frac sleeve. The sleeve 14 slides between the two portions 24, 26. The throughbore 28 extends longitudinally through the sub 12 and sleeve 14 for fluid flow. The ball seat support 16 has an anchoring surface 36 fixedly engaged to the sleeve 14 so that the ball seat support 16 can actuate movement of the sleeve 14. The opposite side of the ball seat support is a seating surface 38. The ball seat holder 18 abuts against the seating surface 38. There are throughbores 40, 50 through the ball seat support 16 and ball seat holder 18, respectively. Fluid can flow through the entire system 10 before the ball 20 is dropped. The ball seat holder 18 includes the mounting member 54 and the ball interface 56. The ball interface 56 ends in holder opening 58. The ball 20 in matched in size to interact with only a particular ball interface 56.

During the steps of flowing more fluid, moving the ball seat holder 18, and sealing the ball 20, fluid pressure builds through the throughbores 28, 40, 50. Pressure increases as the support throughbore 40 and the holder throughbore 50 clamp and eventually close to seal. Fluid passes through the ball seat support 16 and the ball seat holder 18 until the ball 20 is seated. Then, there is a gradual increase in pressure to establish the seal. Fluid flow is not abruptly stopped as the ball is positioned on the ball interface for an immediate seal. In some embodiments, the ball interface 56 narrows slits 70 or other collapsible passageways as the pressure increases and as the ball interface 56 clamps along the tapered portion 46 of the ball seat support 16. Collapsible passageways include slits, overlapping slits, extending panels, or other means. The slits 70 can be arranged in a collet formation also. Fluid flow stops when the collapsible passageways are closed, the ball 20 is set at the holder opening 58, and the ball interface 56 is set at the seat support opening 42. The seal at this stage allows for the next steps of further increasing pressure, moving the sleeve 14, and fracturing at the high temperatures and pressures.

The embodiments of the present invention provide a ball seat system for a multi-stage hydraulic fracturing system. Balls with different sizes are used to trigger corresponding ball seat systems of downhole tools in different zones within a wellbore. The incremental size differences between balls can be reduced, so that more balls can be used for more multiple stages. The risk of ball failure and deformation is reduced, and the differentiation in size between the balls can be reduced. Deformation of the ball is less. The chance for deformation is less, while the ball is still exposed to the high temperature and pressure conditions of fracking.

Embodiments of the present invention are a ball seat system of a ball, ball seat holder, and ball seat support. The seal between the ball, ball seat holder, and ball seat support is improved over the prior art seal between the ball and ball seat. In the present invention, the pressure builds more gradually, as fluid flow through the ball seat system is decreased gradually. The seal is stronger and more stable. There is less risk of damage and failure of the ball on the ball seat because of the added structure. The seal of the embodiments of the present invention withstand fracturing temperatures and pressures. The size and sequence of the balls in multi-stage fracturing are not affected. The same size and sequence can be used, but the seal is stronger at each stage. The embodiments of the present invention allow for safer and more reliable multi-stage fracturing.

The foregoing disclosure and description of the invention is illustrative and explanatory thereof. Various changes in the details of the illustrated structures, construction and method can be made without departing from the true spirit of the invention. 

We claim:
 1. A system for hydraulic fracturing, comprising: a sub with an upper portion and lower portion, said sub having a throughbore extending longitudinally through said sub; a sleeve within said sub, being axially slideable between said upper portion and said lower portion of said sub, said throughbore extending through said sleeve; a ball seat support with a seating surface on one side and an anchoring surface on an opposite side, said anchoring surface being fixedly engaged to said sleeve, said ball seat support being comprised of a support throughbore in fluid connection with said throughbore and a seat support opening at an end of said seating surface; and a ball seat holder disposed within said ball seat support adjacent said seating surface, said ball seat holder being comprised of a holder throughbore in fluid connection and in alignment with said support throughbore of said ball seat support, a mounting member, a ball interface, and a holder opening at an end of said ball interface, said ball interface having a size corresponding to a size of a ball to be received within said ball seat holder so as to form seals between said ball and said ball seat holder and said ball seat support.
 2. The system for hydraulic fracturing, according to claim 1, said sub comprising a plurality of port openings, said sleeve forming a sealed barrier between said throughbore and an annulus of a wellbore in a first sleeve position by covering said port openings, said sleeve forming a fluid connection between said throughbore and an annulus of said wellbore through said port openings, when said sleeve is in a second sleeve position exposing said port openings.
 3. The system for hydraulic fracturing, according to claim 2, said sleeve comprising: a plurality of sleeve ports, forming said fluid connection in said second sleeve position between said throughbore and said annulus through said port openings.
 4. The system for hydraulic fracturing, according to claim 2, said sleeve comprising: a shearing means removably attached to said upper portion of said sub and an exterior of said sleeve, said shearing means being ruptured for movement from said first sleeve position to said second sleeve position.
 5. The system for hydraulic fracturing, according to claim 1, wherein movement of said ball seat support towards said lower portion corresponds to movement of said sleeve toward said lower portion.
 6. The system for hydraulic fracturing, according to claim 1, said seating surface being comprised of a cylindrical portion and a tapered portion, said tapered portion decreasing in diameter from said cylindrical portion to said seat support opening, said seat support opening at an end of said tapered portion.
 7. The system for hydraulic fracturing, according to claim 1, said tapered portion being at least one of a group consisting of conical, arcuate, and curved.
 8. The system for hydraulic fracturing, according to claim 1, further comprising: a seat shearing means removably attached to said seating surface of said ball seat support and an exterior of said mounting member said ball seat holder, said shearing means being ruptured for movement of said ball seat holder towards said seat support opening.
 9. The system for hydraulic fracturing, according to claim 1, wherein said ball seat holder is comprised of a collet collar, said mounting member being a sleeve portion of said collet collar, said ball interface being a clamp portion of said collet collar, said holder opening being a collet opening at an end of said collet collar, said collet opening having a size corresponding to said size of said ball to be received with said ball seat holder.
 10. The system for hydraulic fracturing, according to claim 9, wherein said collet collar has an extended position for receiving said ball, said sleeve portion disposed in a front end of a cylindrical portion of said seating surface, wherein said collet collar has a transitioning position to reduce fluid flow through said holder throughbore, said ball engaging said collet collar, said ball exerting pressure from fluid flow on said collet collar, said ball seat holder shearing from said ball seat support, said ball seat holder moving along said seating surface toward said seat support opening, and wherein said collet collar has a retracted position for sealing said ball, said ball seat holder, and said ball seat support, said holder throughbore being sealed from fluid flow, said collet opening being sealed by said ball, said seat support opening sealed by said collet collar and said ball, said sleeve portion being abutted against said seating surface where said cylindrical portion meets a tapered portion of said seating surface.
 11. The system for hydraulic fracturing, according to claim 1, wherein said ball interface is comprised of tapering collet petals, each petal being separated by slits, wherein fluid flows through said slits, said holder opening, and said seat support opening in an extended position of the collet petals, wherein fluid flow through said slits, said holder opening, and said seat support opening, reduces in a transitioning position of the collet petals, said slits of adjacent collet petals being narrowed, and wherein fluid flow through said slits, said holder opening, and said seat support opening, stops in a retracted position of the collete petals, said slits being closed being adjacent collet petals, so as to form a seal with said ball, the collet petals, and said seat support opening.
 12. The system for hydraulic fracturing, according to claim 11, wherein said tapering collet petals radially overlap, each slit being positioned between and over adjacent petals, and wherein side space between adjacent petals and lateral space between surfaces of adjacent petals are reduced and closed to form said seal.
 13. A system for multi-stage hydraulic fracturing, comprising a first sub with a first upper portion and first lower portion, said first sub having a first throughbore extending longitudinally through said first sub; a first sleeve within said first sub, being axially slideable between said first upper portion and said first lower portion of said first sub, said first throughbore extending through said sleeve; a first ball seat support with a first seating surface on one side and a first anchoring surface on an opposite side, said first anchoring surface being fixedly engaged to said first sleeve, said first ball seat support being comprised of a first support throughbore in fluid connection with said first throughbore and a first seat support opening at an end of said first seating surface; a first ball seat holder disposed within said first ball seat support adjacent said first seating surface, said first ball seat holder being comprised of a first holder throughbore in fluid connection with said first support throughbore of said first ball seat support, a first mounting member, a first ball interface, and a first holder opening at an end of said first ball interface, said first ball interface having a size corresponding to a size of a first ball to be received within said first ball seat holder so as to form seals between said first ball, and said first ball seat holder, and said first ball seat support; a second sub with a second upper portion and second lower portion, said second sub having a second throughbore extending longitudinally through said second sub; a second sleeve within said second sub, being axially slideable between said second upper portion and said second lower portion of said second sub, said second throughbore extending through said sleeve; a second ball seat support with a second seating surface on one side and a second anchoring surface on an opposite side, said second anchoring surface being fixedly engaged to said second sleeve, said second ball seat support being comprised of a second support throughbore in fluid connection with said second throughbore and a second seat support opening at an end of said second seating surface; and a second ball seat holder disposed within said second ball seat support adjacent said second seating surface, said second ball seat holder being comprised of a second holder throughbore in fluid connection with said second support throughbore of said second ball seat support, a second mounting member, a second ball interface, and a second holder opening at an end of said second ball interface, said second ball interface having a size corresponding to a size of a second ball to be received within said second ball seat holder so as to form seals between said second ball, and said second ball seat holder, and said second ball seat support, wherein the first and second throughbores, the first and second support throughbores, and the first and second holder throughbores are in fluid connection to said wellbore, wherein the first and second subs are associated with different downhole tools at different locations in the wellbore, and wherein positions of the first and second subs relate to an order of dropping the first and second balls to respective first and second ball interfaces.
 14. The system for multi-stage hydraulic fracturing, according to claim 13, each sub comprising a plurality of port openings, each sleeve covering said portion openings and forming a respective sealed barrier between each throughbore and an annulus of a wellbore when each sleeve is in a respective initial sleeve position, each sleeve exposing said port opening and forming a respective fluid connection between each throughbore and said annulus of said wellbore when each sleeve is in a respective actuated sleeve position, wherein port openings of each sub for a fluid connection are exposed by respective sleeves at different times.
 15. The system for multi-stage hydraulic fracturing, according to claim 13, wherein each ball seat holder is comprised of a respective collet collar, each mounting member being a respective sleeve portion of each collet collar, each ball interface being a respective clamp portion of each collet collar, each holder opening being a respective collet opening at an end of each collet collar, a first collet opening of said first ball seat holder having a size corresponding to said first ball, a second collet opening of said second ball seat holder having a size corresponding to said second ball, each size of each ball to be received with each ball seat holder being different.
 16. A method for multi-stage hydraulic fracturing, comprising the steps of: installing a downhole tool in a wellbore, said downhole tool being comprised of a sub with an upper portion and lower portion, said sub having a throughbore extending longitudinally through said sub; a sleeve disposed within said sub, being axially slideable between said upper portion and said lower portion of said sub; a ball seat support with a seating surface on one side and an anchoring surface on an opposite side, said anchoring surface being engaged to said sleeve, said ball seat support being comprised of a support throughbore in fluid connection with said throughbore and a seat support opening; and a ball seat holder disposed within said ball seat support adjacent said seating surface, said ball seat holder being comprised of a holder throughbore in fluid connection with said support throughbore of said ball seat support, a mounting member, a ball interface, and a holder opening at an end of said ball interface; flowing fluid through said throughbore of said sub, said support throughbore and said seat support opening, and said holder throughbore and said holder opening; dropping a ball of a set size through said wellbore; seating said ball on said ball interface of said ball seat holder, said set size of said ball corresponding to said ball interface; flowing additional fluid through said throughbore of said sub, said support throughbore, said ball interface and said holder throughbore, increasing pressure of said ball on said ball interface; moving said ball seat holder within said ball seat support toward said seat support opening to a retracted position of said ball seat holder; sealing said ball to said ball interface and said ball seat holder to said ball seat support so as to stop fluid flow through said holder opening, said ball interface, and said seat support opening; flowing more fluid through said throughbore of said sub, increasing pressure of said ball seat support on said sleeve; sliding said sleeve between said upper portion toward said lower portion by fluid pressure on said ball, said ball seat holder, and said ball seat support, said ball seat support abutting against said sleeve; opening access of frac ports in said wellbore to said throughbore; and fracturing hydraulically through said frac ports at a pressure maintained by sealing said ball to said ball interface and said ball seat holder to said ball seat support
 17. The method for multi-stage hydraulic fracturing, according to claim 16, further comprising the steps of: completing a fracturing at said downhole tool; dropping another ball of another set size through said wellbore, said set size of said ball being different from said another set size of said another ball; seating said another ball on another ball interface of another ball seat holder of another downhole tool in another location in said wellbore, said another set size of said another ball corresponding to said another ball interface; fracturing hydraulically through another frac port at a pressure maintained by sealing said another ball to said another ball interface and said another ball seat holder to another ball seat support of said another downhole tool.
 18. The method for multi-stage hydraulic fracturing, according to claim 16, wherein said set size of said ball corresponds to only one ball interface of any ball seat holder in said wellbore.
 19. The method for multi-stage hydraulic fracturing, according to claim 16, wherein the step of sealing said ball to said ball interface and said ball seat holder to said ball seat support comprises: reducing fluid flow through said ball interface by narrowing slits in said ball interface; and stopping fluid flow through said ball interface by closing said slits in said ball interface.
 20. The method for multi-stage hydraulic fracturing, according to claim 19, wherein said slits of said ball interface are arranged in a collet formation. 